Researchers create system that allows amputees to 'feel' with prosthetic hands

Wednesday

Oct 8, 2014 at 12:01 AMOct 9, 2014 at 5:45 AM

Cotton balls always have given Igor Spetic the heebie-jeebies - so much so that he asked family members to open medicine bottles and remove them. So Spetic, 48, of Madison in northeastern Ohio, knew exactly what caused the hairs on his arm to rise when a researcher brushed the back of his prosthetic hand.

Encarnacion Pyle, The Columbus Dispatch

Cotton balls always have given Igor Spetic the heebie-jeebies — so much so that he asked family members to open medicine bottles and remove them.

So Spetic, 48, of Madison in northeastern Ohio, knew exactly what caused the hairs on his arm to rise when a researcher brushed the back of his prosthetic hand.

“I knew immediately that it was cotton,” said Spetic, who was blindfolded.

Spetic couldn’t actually feel the cotton ball, but in a way he did, thanks to a promising new sensor-laden prosthetic system that ties into the nerves in his arm and shoots a message to his brain.

The experimental system is limited to the lab at this point, but it shows promise for everyday use someday, say the scientists who created it at Case Western Reserve University and the Cleveland Veterans Affairs Medical Center.

The system uses electrical stimulation to give amputees such as Spetic the sense of touch again and, in some cases, the ability to distinguish textures.

“The sense of touch is one of the ways we interact with objects around us,” said Dustin Tyler, an associate professor of biomedical engineering at Case Western Reserve and director of the research.

“Our goal is not just to restore function but to build a reconnection to the world.”

The system also has had an unexpected benefit, Tyler said.

Spetic said he no longer feels the phantom pain that once plagued him. He said it used to feel as if a vise were crushing his closed fist.

By placing electrodes on Spetic’s nerves in his forearm, researchers are able to send signals to his brain. That creates a response that makes it seem as though his prosthetic hand can feel, Tyler said.

“The perception of touch occurs in the brain, not in the hand ... so losing the limb is really losing the switch that turns that sensation on or off,” he said.

Instead of threading electrodes directly into the nerves — other scientists have done that — the Cleveland researchers developed small cuff-like electrodes that encircle major nerve bundles in the arms.

“We want to get access to as much of the nerve as we can without actually penetrating into it,” Tyler said.

He said many scientists worry that threading electrodes through or along the nerves can damage them.

Surgeons ran lead wires under the skin and out the upper arm of Spetic and another patient, both of whom lost their hands in industrial machinery, said Matthew Schiefer, a researcher at the Cleveland VA Medical Center and an instructor at Case Western Reserve.

Spetic has three electrode cuffs in his forearm that enable him to feel sensations in 19 distinct points along his prosthetic wrist and hand. The other participant, Keith Vonderhuevel, 48, of Sidney, has two cuffs in his upper arm, enabling him to feel 16 locations.

Schiefer said current stimulation patterns create a tingling pattern. To provide more natural sensations, he said, the research team developed algorithms that convert the input from sensors taped to the patients’ hand into varying patterns and intensities of electrical signals.

The different signal patterns, passed through the cuffs, are read as different stimuli by the brain. Participants have described feeling pressure, tapping, vibration and a brushing movement along their prosthetics, he said.

“One time, I had the distinct feeling of water trickling down the back of my hand,” said Vonderhuevel. “It was crazy.”

Spetic can discern rough, smooth and ridged surfaces, Schiefer said. When researchers touched two different textures on two locations at the same time, Spetic was able to differentiate them.

Tyler said he thinks that people create a map of sensations throughout their lives that allows them to interpret signal patterns as different sensations. This system, he said, allows the amputees to tap into those memories.

“I don’t presume the stimuli we’re giving is hitting the spots on the map exactly, but they’re familiar enough that the brain identifies what it is,” he said.

The pressure sensors mounted to the participant’s prosthetic hands also allow them do such things as gently pull stems from cherries without crushing them, or shake someone’s hand.

Vonderhuevel said this would help with his cooking and allow him to play with his grandchildren.

“The kids love me to push their noses with my prosthetic, and I don’t want to hurt them,” he said.

While perceived sensations can fade in a matter of weeks in other systems, the Cleveland technology has proved stable over the long run, Schiefer said. The system has worked for 21/2 years in Spetic and 11/2 years in Vonderhuevel.

Tyler said he hopes his team can develop a system within five years or so that amputees can use at home.

Vonderhuevel, an Army veteran, said he hopes the technology will make a difference for the many military men and women who return home from service missing limbs.

“I’m doing it for them,” he said.

The work was published yesterday in the journal Science Translational Medicine.